In an injection stretching blow molding machine disclosed, for example, in the present inventor's U.S. Pat. No. 4,105,391, wherein a rotary disk is provided on the under-side of a base plate, the required number of neck molds are attached to the under-surface of and parallel to a tangent line of the rotary disk, and an injection molding mold, a temperature control member and a blow mold are disposed between the rotary disk and a machine bed, whereby when the rotary disk is stopped, the steps of injection molding parisons, temperature controlling, stretching blow molding hollow molded products and releasing are carried out. The blow mold and a mold closing mechanism are located between the rotary disk and a lower base plate which forms a part of the machine bed. This blow mold is opened and closed in a diametrical direction of the rotary disk by a mold opening and closing mechanism secured to the lower base plate, and in the state where the mold is open, laterally receives the neck mold parallel to the tangent line. When the rotary disk is stopped, the mold is closed by the mold opening and closing mechanism from both sides of the neck mold.
However, where a plurality of neck molds are provided, they are arranged in a linear fashion, and the neck molds and parisons held thereon are transported in the form of circular motion, and thus, the distance that the blow molds must be moved into their open positions becomes great in order to prevent them from contacting the blow molds. Further, the opening and closing mechanism for the blow molds is merely secured to the lower base plate, which mechanism is a mechanism uncapable of installing a tie bar to receive a mold closing reaction, that is, a reaction relative to the mold closing being a cantilever mechanism, and therefore, the mold closing force in an upper portion close to the neck mold is inevitably weak and in blow molding, the upper portion of the blow mold tends to open more than the lower portion thereof, which poses a disadvantage in that a parting line of the upper portion of a molded product becomes somewhat thick.